Move all screen-splitting-related selectors to atom.css

static/atom.css

@@ -31,11 +31,19 @@ body {
   position: relative;
 }
 
-.horizontal > .vertical {
+.horizontal > div {
   width: -webkit-flex(1);
+  height: auto;
 }
 
-.vertical > .horizontal {
+.vertical > div {
   height: -webkit-flex(1);
 }
 
+.horizontal > * + * {
+  border-left: 5px solid #515151;
+}
+
+.vertical > * + * {
+  border-top: 5px solid #515151;
+}

static/editor.css

@@ -8,23 +8,6 @@
   -webkit-user-select: none;
 }
 
-.horizontal > .editor.split {
-  width: -webkit-flex(1);
-  height: auto;
-}
-
-.horizontal > .editor.split + .editor {
-  border-left: 5px solid rgba(255, 255, 255, .15);
-}
-
-.vertical > .editor.split {
-  height: -webkit-flex(1);
-}
-
-.vertical > .editor.split + .editor {
-  border-top: 5px solid rgba(255, 255, 255, .15);
-}
-
 .editor .scrollable-content {
   display: -webkit-flexbox;
 }